The LSAC has published statistical evidence comparing results from different forms of LSAT Prep. The data showed that use of commercial test prep courses (such as ScoreItUp LSAT Prep) led to more improvement, on average, than “self-study” or undergraduate LSAT Prep courses.
The statistical data, of course, is incomplete and should not be relied upon as a guarantee. Nevertheless, the findings by the LSAC (see the middle column of Table 13 on page 21 for a quick reference of the data) are worthy of consideration. The data also provides some statistical evidence demonstrating what many in the industry have observed empirically.
You also can read an article further analyzing the LSAC’s data on this issue here.